1. Field of the Invention
This invention relates to a process of making silicone sealants of alkoxysilethylene endblocked polydiorganosiloxane and precipitated calcium carbonate fillers which have improved adhesion to substrates.
2. Background Information
Silicone sealants which cure through a neutral reaction are known in the art. Examples can be found in U.S. Pat. No. 3,856,839, issued Dec. 24, 1974, disclosing alkanedioxy titanium chelates which catalyze the cure of a composition which also contains methyltrimethoxysilane and a silanol chain-stopped polydiorganosiloxane fluid; and U.S. Pat. No. 4,143,088, issued Mar. 6, 1985, disclosing use of alkoxylated organosilicon compounds consisting of either monomers or polymers having difunctional, trifunctional, or tetrafunctional molecules, comprising at most 40 percent of difunctional monomers in an organosilicon composition which is storage stable in the absence of moisture and is rapidly curable into elastomers with self-adherent properties in the presence of water at room temperature.
The sealants such as described in these references have a tendency to require a longer time to cure as they shelf age. In some cases, the sealant arrives at a point where it no longer cures upon exposure to moisture. This is particularly serious, because the user does not realize the problem until after the sealant is put into place. To correct the problem, all of the uncured sealant must be removed and replaced, a very time consuming and expensive undertaking.
A method of improving the storage stability is shown in U.S. Pat. No. 4,687,829, issued Aug. 18, 1987. An improved sealant is produced by mixing alkoxy functional polydiorganosiloxane having alkoxysilethylene ends with a combination of trifunctional or tetrafunctional silane crosslinker and difunctional silane chain extender. A method of producing such a sealant having an in situ treated filler is taught in U.S. Pat. No. 4,711,928, issued Dec. 8, 1987.
Neutral curing sealants having reinforcing silica fillers have been produced which have a low modulus, but their adhesion to concrete has been marginal. A need exists for a low cost neutral sealant having good adhesion to a variety of substrates.